This invention relates to a navigation system for a vehicle that assists the driver to guide the vehicle along a route to a destination.
In existing navigation systems based on route guidance, a suitable display helps the driver direct the vehicle to the destination. In such a navigation system, a road map is stored in a memory unit. When the driver enters the vehicle's current position and its destination, the system calculates a route to the destination and guides the driver along the route. The system gives the driver directions, such as "go straight," "turn left," "turn right," etc., well before the vehicle passes through the intersection where the driver must carry out the maneuver.
Such a conventional navigation system is disclosed, for example, in Japanese Laid-open Patent Publication No. 62-91811, in which an optimal route is computed between two designated places. When the destination is not a discrete place, the conventional navigation system either cannot guide the driver or can do so only with considerable inconvenience, because routes to a plurality of destinations must be calculated in sequence one after another and then compared. For example, the driver may wish to go to the nearest branch of a particular bank, e.g., Bank of America, or to the nearest of a chain of stores, e.g., K-mart. He may know where he wants to go only by what he needs rather than by location, e.g., the nearest hardware store. Further, when the vehicle's starting point is not on a road, e.g., the vehicle starts from a parking lot, its location with reference to a road network becomes uncertain, so that there exist a number of optional starting points. The conventional vehicle navigation system has great difficulty with any of these cases.